EXCEED THE SPACE PROVIDED. Ozone is a ubiquitousurban air pollutant known to cause decreases in respiratory function, airway hyperreactivity and alveolar epithelial injury in humans and experimental animals following acute exposure. This is associated with an inflammatory response characterized by increased numbers of macrophages in the lung. During the past several years, we have generated data that directly supports the model that these cells become "activated" and release cytotoxic anc proinflammatory mediators that contribute to the pathogenesis of lung injury. Thus, following exposure of animals to ozone, we foundthat alveolar macrophages are "activated"to release proinflammatory cytokines including tumornecrosis factor-a (TNFa), interleukin-1P (IL-1P) and interferon-y (IFNy), and cytotoxic mediators inparticular, nitric oxide,which has been directly implicated intoxicity. Furthermore, we demonstrated that blocking macrophages, TNFa or nitricoxide generation abrogates ozone-induced tissue injury. Surprisingly,duringthe course of our studies we discovered that Type II alveolar epithelial cells also become "activated" following ozone exposure. In fact these cells acquire physicalanc functional properties of inflammatory macrophages and they may also contribute to tissue injury. The overall objective of the studies outlined in this application is to analyze mechanisms underlying increased production of nitric oxide by macrophages and Type II cells in the lung following ozone inhalation. We hypothesize that inhalationof ozone leads to increased expression and/or prolonged activity of key cytokine-inducibletranscription factors: NF-KB, STAT-1 and IRF-1 These transcription factors act cooperatively to regulate nitricoxide production via induction of the enzyme, nitric oxide synthase II. This leads to excessive nitric oxide production and toxicity. To test this hypothesis, studies are planned to: (1) analyze the role of NF-KB, STAT-1 and IRF-1 in ozone-induced increases in nitric oxide production and toxicity; and (2) examine biochemical mechanisms leading to alterations in transcription factor activity following ozone inhalation. The results of these studies will advance our understanding of how inhalation of ozone leads to the generation of inflammatory mediators in the lung and may help identify molecular/biochemical targets for therapeuticintervention.